Patent document 1 describes a method for the treatment and prevention of metabolic disorders and other diseases by administering a pyrone analog, or a derivative thereof, in combination with one or more additional agents such as, for example, lipid lowering agents or glucose lowering agents. As one of the examples of the pyrone analog, taxifolin is described and, as one of the examples of the glucose lowering agent, metformin is described. However, this document does not disclose any specific example of a combination of metformin and taxifolin, and does not describe a synergistic effect against malignant tumors or a lactic acidosis-lowering effect of a medicament containing them in combination.